When not in use, sliding panels (particularly if external to the building, such as patio doors) need to be lockable for security. However, for ease of use, when unlocked they are made so as to be freely slidable in their surrounding framework.
During closing of a patio door, any person interposing for instance their hand or fingers between the leading edge(s) or leading edge surface of the door and the closure jamb of the framework can be seriously injured; it is known that such fingertip injuries are most commonly suffered by children, typically either acting alone or when an adult has inadvertently or accidentally quickly closed the door.
The door lock mechanism is typically face-mounted on the door leading edge, and comprises an espagnolette with mushroom headed security bolts intended to engage behind narrowed portions of keyhole slots in the closure jamb; inquisitive children in particular are known to interfere with and misuse the lock and then to seek to close the door with the mushroom headed security bolts already in the locked position, so damaging the locking mechanism in whole or in part, and affecting the security offered by the door.